The principal objective of this study is to determine the effect of ethanol on the metabolism of neurosteroids in the central nervous system. Neurosteroids such as 5a-pregnane-3a-ol-20-one (5a,3a-THP or Allopregnanolone) and 5a-pregnane-3a,21-diol-20- one(THDOC) have been shown to modulate the GABA/benzodiazepine binding sites and to exert anxiolytic and hypnotic effects. Modulation of these neurosteroids in the central nervous system by ethanol may be one of the underlying mechanisms for stress observed in human alcoholics especially during withdrawal. The GC/MS-NCI technique that we previousely established for the measurement of trace levels of neurosteroids in human cerebro spinal fluid (CSF) has been extended to the analysis of rat tissue samples and human plasma in this period. We were able to establish a procedure to quantify pregnenolone, 5a,3a-, 5b,3a-, 5a,3b-THP, and dihydrotestosterone, dihydroprogesterone and progesterone in these samples. Using this technique, we are in the process of studying the effect of ethanol on the neurosteroid levels in brain tissues.